1. Field of the Application
The present application generally relates to a communication system, and more particularly, to a method of setting up a connection in a communication system and a radio network controller (RNC) and the communication system using the same.
2. Description of Related Art
In a conventional cellular radio system, a user equipment (UE, a handheld communication device, such as a cell phone) communicates with the core network (CN) through a radio access network (RAN).
Conventionally, when a UE is about to set up a connection with a CN through a Node B, the UE sends a radio resource control (RRC) connection request to the base state to set up the connection, wherein the Node B may be an eNodeB in a LTE RAN network structure or a NodeB in a WCDMA RAN network structure. Below, a radio network controller (RNC) of a WCDMA network structure will be described as an example.
FIG. 1A is a flowchart illustrating how conventionally a UE sets up a RRC connection with a RNC, wherein the RRC connection is successfully set up. As shown in FIG. 1A, when the UE is about to enter a connected mode from an idle mode, the UE sends a RRC connection request message to the RNC. Then, the RNC sends a RRC connection setup message back to the UE. After that, the UE further sends a RRC connection setup complete message to the RNC. By now, the UE successfully enters the connected mode from the idle mode.
FIG. 1B is another flowchart illustrating how conventionally a UE establishes a RRC connection with a RNC, wherein the setup of the RRC connection fails. Referring to FIG. 1B, after the UE sends the RRC connection request message to the RNC, the RNC sends a RRC connection reject message back to the UE if the RNC rejects the request of the UE due to some reasons (for example, in consideration of load balance). Thereby, the UE cannot set up the RRC connection with the RNC successfully and accordingly cannot enter the connected mode from the idle mode.
Besides controlling a RNS, a RNC may further be connected to a plurality of Nodes B, and each of the Nodes B serves a macro cellular cell (referred to as a macro cell thereinafter), wherein the macro cell is served by an outdoor Node B, while an indoor Femto cellular cell (referred to as a Femto cell thereinafter) is served by an indoor Femto access point (FAP).
A FAP (also known as a home Node B) is a small and low power cellular cell typically designed for use in a home or small business. A FAP extends the service area of a cellular network indoors to provide voice and data services to users. A FAP looks similar to a wireless fidelity (Wi-Fi) access point (AP) and which can be either used independently or integrated with a home gateway as a part of a home network.
Generally speaking, an indoor UE may still use the service provided by an outdoor Node B if the signal received from the outdoor Node B is good. However, in this case, the indoor Node B is not used.
FIG. 2 is a diagram of a conventional mobile communication network structure. As shown in FIG. 2, the communication network structure 200 includes a macro cell 210, a macro cell 220, a broadband access device 230, an IP network 240, a Femto gateway (Femto GW) 250, a CN 260, and a RAN 270. The macro cell 210 includes a Node B 214, wherein the Node B 214 performs wireless communication with a UE 212 so that the UE 212 can communicate with the CN 260 through the RAN 270.
The macro cell 220 contains a Femto cell 222, and the Femto cell 222 includes a FAP 222a. The UE 212 connects to the FAP 222a when it moves from the macro cell 210 to the Femto cell 222. The FAP 222a then connects to the IP network 240 through the broadband access device 230 of an indoor wired broadband network and further connects to the CN 260 through the Femto GW 250.
The technique described above of connecting to a wireless mobile network through a wired broadband network by using the FAP 222a allows less outdoor Nodes B to be deployed. In addition, since the FAP 222a has a lower transmission power, the transmission power of a cell phone is also lowered.
However, when the UE 212 which is in a communication session moves from an outdoor place (i.e., the coverage area of the macro cell 210) to an indoor place (i.e., the coverage area of the Femto cell 222), the UE 212 does not try to detect the FAP 222a if the signal provided by the macro cell 210 is strong enough. Besides, the UE 212 which is in an idle mode does not try to detect the FAP 222a if it receives a strong signal from the macro cell 220. Thereby, how to allow the UE 212 in the idle mode to detect the FAP 222a when the UE 212 needs to communicate with the CN 260 has become one of the major subjects in the industry.